This application claims the priority of German Application No. 198 29 583.9, filed Jul. 2, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for determining the breakdown voltage during the ignition of an internal-combustion engine and to an apparatus for performing the process.
German Patent Document DE 27 52 244 A1 describes, for example, a process and apparatus for testing an electric ignition. For rapidly testing the component parts in their operative position, the time sequence of the voltage is measured on the primary winding side and/or on the secondary winding side. On the basis of the voltage time sequence, a conclusion is drawn, for example, about the spark gap or concerning moisture in the distributor. A current drop which is too fast indicates a spark gap which is too large, corresponding with electrode consumption. A current drop which is too slow, in contrast, indicates a spark gap which is too small. The course of the voltage in the secondary winding can also be measured by the falling voltage in the primary winding.
In German Patent Documents DE 30 41 498 A1 and DE 40 37 071 A1, it is suggested to detect the breakdown point in time during the ignition and, as a function thereof, draw a conclusion concerning the condition of the ignition system. In German Patent Document DE 30 41 498 A1, a negative flank pulse is generated at the point in time of the ignition, which flank, by way of a coupling capacitor and a comparator, resets a flip-flop. The comparator is used for recognizing this negative impulse. The tapping of the ignition signal takes place on the primary side. In German Patent Document DE 40 37 071 A1, a conclusion is drawn about the quality of the ignition system from the time period which passes between the rise of the primary voltage of the ignition coil and the lowering of the current in a limiting circuit. For this purpose, the point in time of the rise of the primary voltage of the ignition coil is determined. This rising point in time is caused by the switching-off of the switching transistor in the range of the ignition point in time. The point in time of the falling of the current in the limiting circuit is determined. This falling point in time is caused by the spark discharge at the ignition point in time.
German Patent Document DE 43 03 030 A1 discloses a method and a system for monitoring the ignition behavior in the case of capacitance discharge ignition systems. In this case, the ignition voltage required for igniting a spark plug is determined from the duration of the current flow through the ignition coil primary winding. Since the coil coupling is low in the case of alternating-voltage ignitions, however, a qualitative measurement of the current change and/or voltage change on the primary side of the ignition is not possible. In the case of alternating-voltage ignitions, for the direct measurement of the breakdown voltage on the secondary side, a high-voltage sensing probe is therefore used. However, a high-voltage sensing probe is expensive.
It is an object of the invention to provide an inexpensive and simple process for determining the breakdown voltage and thus diagnosing the engine and testing the ignition system.
According to the invention, this object is achieved by a process for determining the breakdown voltage in the case of the ignition of an internal-combustion engine, characterized in that the breakdown point in time is determined and the breakdown voltage is determined based on the breakdown point in time. A system for performing the method is characterized in that the detection of the breakdown point in time is carried out by a time-dependent current or voltage measurement either on the primary side of the ignition system at a measuring point, which is situated at the connection of the ignition coil primary winding not connected with the supply voltage, or on the secondary side of the ignition system on the low-voltage side at other measuring points.
Advantageous further developments of the object of the invention are described herein.
An important advantage of these further developments is the fact that the voltage measurement is only qualitatively carried out. The value of the breakdown voltage is not measured directly but only the breakdown point in time is determined by measuring the voltage. By detecting the breakdown time, the breakdown voltage is determined in a simpler and more precise manner. This simplifies any type of testing of the ignition system or of the engine diagnosis during which the breakdown voltage is used as an indicator. Because of its precision, a qualitative measuring of the voltage or of the current is advantageous. For this reason, the amount of time before the breakdown is determined. Since at the ignition point in time, the voltage breaks through at the electrodes of the spark plug and there is a large current flow, a large drop of the voltage takes place at the spark plug at the ignition point in time. Since the voltage drop at the ignition point in time can be determined very intensively and therefore precisely, it is advantageous, particularly in the case of alternating-voltage ignitions, that, on the primary side, the measuring the voltage provides an informative value of the breakdown time and thus of the breakdown voltage.
In the case of alternating-voltage ignitions, because of the low coil coupling, the breakdown voltage on the primary side cannot be measured quantitatively. However, it is possible to recognize the abrupt voltage drop at the ignition point in time by measuring the voltage on the primary side. The breakdown point in time is detected by way of the voltage drop. However, a direct measurement of the breakdown voltage from a voltage measurement is not possible. By comparing, in an engine control unit (ECU) for example, the detected breakdown point in time with a time-dependent characteristic voltage diagram determined previously in an empirical or theoretical manner, the breakdown voltage is determined very precisely.
By means of the breakdown voltage, all other factors which depend on the breakdown voltage can be determined. These include, in particular, the testing of the ignition system as well as the direct engine diagnosis. As a result of the determination of the breakdown voltage, a spark plug diagnosis in a cold test as well as during engine operation can be carried out. Furthermore, the engine tightness can be tested in the cold test. In addition, the combustion space pressure can be determined during the cold test and during the operation of the engine. The determination of the spark gaps and the testing of the spark plugs with respect to an insulator breakage can also be carried out by means of determining the breakdown voltage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.